1. Field of the Invention
The present invention relates to solid state lasers and frequency shifting of laser output. More specifically, the present invention relates to systems and method for frequency shifting solid state laser output into the 2.5-3.0 micron range.
2. Description of the Related Art
Lasers are currently widely used for communication, research and development, manufacturing, directed energy and numerous other applications. For many applications, the energy efficiency, power and lightweight of solid state lasers makes these devices particularly useful. Because only a few crystals lase and each crystal lases at a unique fundamental frequency, the wavelengths which can be generated by a laser are limited.
Efficient generation of pulsed tunable laser output in the 2.5-3.0 micron region has been particularly difficult to achieve. Direct laser sources in this region are inefficient and lack true continuous tunability. A system which can generate strong coherent output at these wavelengths would be useful for many potential applications such as remote chemical sensing, biological agent detection, and infrared countermeasures. It could also be used as a pump source for generating lasers at longer wavelengths.
Furthermore, it would be useful if such a system was continuously tunable. A problem associated with the use of lasers at these wavelengths has been the tendency of the moisture in the atmosphere to absorb energy at certain wavelengths in this region, making it difficult to propagate energy over long distances. A series of water absorption bands exist in the 2.5-3.0 micron region which are very sharp and narrow. A continuously tunable laser could be used to alleviate this problem by allowing one to move the output wavelength to one side or the other of a particular water absorption spike.
Hence, there is a need in the art for a system or method for efficient generation of pulsed tunable laser output in the 2.5-3.0 micron region.
The need in the art is addressed by the system and method of the present invention. In a most general sense, the invention is an arrangement comprising a mechanism for shifting energy received at a first wavelength and outputting the shifted energy at a second wavelength. The second wavelength is a secondary emission of energy induced by a primary emission generated from the first wavelength in the shifting medium. Hence, a novel feature of the invention is the inclusion of a second mechanism, in functional alignment with the first mechanism, for containing the primary emission and enhancing the secondary emission. This constrains the energy to be output by the arrangement at the desired wavelength.
In addition, the first mechanism is angle tunable, such that the output wavelength can be continuously tuned by varying the angle of the incoming energy at the first wavelength relative to the first mechanism.
In the illustrative embodiment, the first mechanism is an optical parametric oscillator having a crystal such as potassium titanyl arsenate. The crystal may be X-cut, Y-cut, etc. The second mechanism then includes first and second reflective elements. The first and second reflective elements have high reflectivity at a wavelength of the primary emission. The first reflective element also has high reflectivity at the second wavelength of the secondary emission, and the second reflective element is at least partially transmissive at the second wavelength of the secondary emission.
In one embodiment illustrated herein, the first wavelength is approximately 1.06 microns, the second wavelength is approximately 2.59 microns and the primary emission includes energy at 1.53 microns.
Thus, the present invention provides a novel system and method for generating tunable pulsed laser output at 2.59 microns by converting the output of a standard 1 micron laser using a tunable monolithic serial optical parametric oscillator.